Metal cleaning process



Feb. 13, 1962 F. G. SCHUMACHER 3, 1,

METAL CLEANING- PROCESS Filed June 4, 1957 2.: v \9 l1 0 Z! a A 8 INVENTOR.

F'rederlck G. schumaoher ATTGRNEY United States Patent 3,021,235 METAL CLEANING PROCESS Frederick G. Schumacher, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 4, 1957, Ser. No. 663,454 1 Claim. (Cl. 134-26) This invention relates to an apparatus and method for cleaning metal or other non-porous articles to remove various types of soil including materials that are soluble in either non-aqueous solvents or water. It relates particularly to a cleaning system utilizing cold chlorohydrocarbon degreasing solvents and water.

In the past, dip cleaning processes have been employed with chlorohydrocarbons as well as with aqueous cleaners. However, in many processes, satisfactory results cannot be obtained with either aqueous or non-aqueous solvents when used alone. Such treatments often leave an insoluble residue which is subsequently diflicult to remove with any cleaning technique. The use of spray at ambient temperatures in degreasing is unsatisfactory because a spray force sufiicient to insure cleaning cannot be used without excessive solvent losses due to evaporation and mist. Solvent loss is not a problem in hot degreasers where spraying is carried below the vapor line of a boiling solvent. However, another difficulty lies in the fact that the high solvent temperatures normally employed in degreasing sometimes cause the soil to bake or set up on the work making it more diflicult to remove.

It is the general object of this invention to provide an apparatus for an efiective, economical method for cleaning articles with water and a chlorohydrocarbon degreasing solvent at ordinary or low temperatures.

Another object is to provide cleaning process employing a spray of chlorohydrocarbon degreasing solvent and a water dip in such manner that a minimal quantity of chlorohydrocarbon is used.

Another object is to pr )vide apparatus for cleaning with water and a chlorohydrocarbon degreasing solvent with means for substantially complete recovery of the chlorohydrocarbon solvent.

Other objects will become apparent in the following discussion.

In general, the objects of this invention are accomplished by passing articles under the surface of an aqueous bath and then up into a completely Water-sealed dome where they can be thoroughly sprayed with a chlorohydrocarbon degreasing solvent. The solvent is then recovered as a lower layer from the bottom of the aqueous bath.

The invention is illustrated in greater detail by the accompanying drawing. This shows a vertical section of the tank and the inverted tank or treating dome 11. As indicated the tank contains water 12 and a small bottom layer of chlorinated degreasing solvent 13. The work 20 is carried through the tank by hooks 21 on a chain conveyor 18 mounted on sprocket wheels 19. As indicated the work enters at the left through the water seal into the dome 11 where it is sprayed with solvent from the sprayhead 17. The used solvent then descends ice into the water to form the aforesaid under layer 13 a portion of which passes through valve 24 and line 14 to pump 15 and then passes to the spray-head through line 16. A purge stream of dirty solvent is removed continuously through line 23 for purification. Fresh or recovered solvent enters the system as needed through line 22. Solvent sprayed work is removed through the water seal on the right side of the tank as indicated. Alternatively, valve 24 may be closed so that only clean solvent is fed to the pump through line 22.

As will be evident to anyone skilled in the art, numerous variations can be made in the apparatus without departing from the invention illustrated. Numerous spray-heads arranged at various angles can be substituted for the one shown. The tank can be designed to provide a sediment zone at the bottom which can be cleaned out from time to time. Work covered with sand, grit, loose particles of metal, etc. will make it necessary to arrange for sediment removal. A filter in the solvent recirculation line may also prove necessary.

Small amounts of cleaning compounds, surface-active agents etc. may be added tn the water or the degreasing solvent to make the cleaning action more efiicient provided these agents do not cause the formation of a stable emulsion of solvent and water. In general solvents with a density exceeding that of water, preferably by at least about 25%, are required. These solvents should have a good degree of chemical stability and may contain small amounts of stabilizing agents. The preferred solvents are trichlorethylene, perchlorethylene and methylene chloride. The preferred operating temperatures are ordinary tem peratures in the range 10 to 40 C.

Having described my invention, I claim:

The process of cleaning non-porous, surface contaminated articles at ambient temperatures with water and a chlorinated hydrocarbon solvent comprising, providing a tank having an upper layer of water and a lower layer of a chlorinated hydrocarbon solvent selected from the group consisting of trichloroethylene, perchloroethylene, and methylene chloride, conveying said articles into said tank through the upper layer of water into a completely water-sealed air dome, spraying said articles with said chlorinated hydrocarbon solvent in said air dome over said water layer said chlorinated hydrocarbon solvent settling to the bottom of said tank for subsequent reuse, and conveying said articles out of said air dome through the upper layer of water.

References Cited in the file of this patent UNITED STATES PATENTS 448,895 Van Kannel Mar. 24, 1891 2,022,201 Herold Nov. 26, 1935 2,270,642 Somcs Jan. 20, 1942 2,273,939 Dammers Feb. 24, 1942 2,310,569 Booth Feb. 9, 1943 2,689,198 Judd Sept. 14, 1954 FOREIGN PATENTS 57,525 Denmark Apr. 8, 1940 400,613 Great Britain Oct. 23, 1933 

